Lichen-rich coastal and inland sand dunes (Corynephorion) in the Netherlands: vegetation dynamics and nature management Promotor: Prof. dr. K.V. Sýkora Hoogleraar Ecologische Inrichting en Beheer Infrastructuur, Wageningen Universiteit Samenstelling promotiecommissie: Prof. Dr. A.M. Cleef, Wageningen Universiteit Prof. Dr. F.J.A. Daniëls, Universität Münster Dr. H.J. During, Universiteit Utrecht Prof. Dr. M. Hoffmann, Universiteit Gent Dr. P.C. de Hullu, Directie Kennis Ministerie van LNV Dit onderzoek is ingeschreven bij de onderzoeksschool SENSE Lichen-rich coastal and inland sand dunes (Corynephorion) in the Netherlands: vegetation dynamics and nature management Henderika Gepke Maria Oostra Proefschrift ter verkrijging van de graad van doctor op gezag van de rector magnificus van Wageningen Universiteit, Prof. Dr. M.J. Kropff in het openbaar te verdedigen op vrijdag 3 november 2006 des namiddags te vier uur in de Aula Rita Ketner-Oostra (2006) Lichen-rich coastal and inland sand dunes (Corynephorion) in the Netherlands: vegetation dynamics and nature management. PhD Thesis, Wageningen University and Research Centre ISBN 90-8504-514-2 Copyright © Rita Ketner-Oostra Table of Contents Chapter 1. General introduction 3 Chapter 2. Decline of lichen diversity in calcium-poor coastal dune vegetation since the 1970s, related to grass and moss encroachment 15 Chapter 3. Vegetation succession and lichen diversity on dry coastal calcium-poor dunes and the impact of management experiments 45 Chapter 4. Restoration of lichen diversity in grass-dominated vegetation of coastal dunes after wildfire 75 Chapter 5. Will we lose the last active inland drift sands of Western Europe? The origin and development of the inland drift-sand ecotype in the Netherlands 93 Chapter 6. Long-term vegetation succession in lichen-rich drift sand in the central Netherlands as influenced by habitat restoration 119 Chapter 7. Synthesis 161 Summary 181 Samenvatting 187 Curriculum vitae 193 Dankwoord 197 Chapter 1 LICHEN-RICH COASTAL AND INLAND SAND DUNES (CORYNEPHORION) IN THE NETHERLANDS: VEGETATION DYNAMICS AND NATURE MANAGEMENT General introduction Rita Ketner-Oostra 2 Chapter 1. General introduction 1.1. Lichen-rich grasslands in nutrient-poor sand dunes in the Netherlands before the 1970s Until the mid-1970s the dry coastal calcium-poor dunes in the phytogeographical Wadden district in the Netherlands (van der Meijden 1996) were famous for their lichen-rich pioneer grasslands, developed in the course of primary succession in the xeroseries (Westhoff 1947). The greater part of the older dune slopes was covered by a short grassland, the Violo-Corynephoretum Westhoff ex Boerboom 1960 (V.- C.), dominated by grey hairgrass (Corynephorus canescens) and sand sedge (Carex arenaria) and rich in the lichen genera Cladonia and Cladina, the latter called reindeer lichens. These lichen-rich ‘grey dunes’ were especially well developed on the island of Terschelling (Brand & Ketner-Oostra 1983). Lichens that are usually epiphytic, such as Bryoria fuscensens, Evernia prunastri, Hypogymnia physodes, H. tubulosa, Pseudevernia furfuracea and Usnea spp., grew on moss carpets, but also on open sites with only Corynephorus canescens (Barkman 1958; Ketner- Oostra 1972). Apart from these calcium-poor coastal dunes, there are considerable areas of non- calcareous inland sand dunes in the Netherlands originating from Pleistocene deposits (Koster 2005). Many of these once large areas have been reduced in size since the late 19th and early 20th centuries as a result of afforestation. One of the largest remaining areas of these semi-natural inland sand-dune ecotopes is the Kootwijkerzand. Here, short pioneer grasslands with C. canescens assigned to the Spergulo-Corynephoretum Libbert 1932 (S.-C.) are part of the xeroseries. Until the 1970s the intermediate and terminal succession stages and the spatial gradients to heath were rich in the lichen genera Cladonia and Cladina. The relation between vegetation, soil and microclimate in these heathlands and inland dunes was studied by Stoutjesdijk (1959). An integrated research and teaching training project of the University of Utrecht (Department of Vegetation Science of the Institute of Systematic Botany) on inland and coastal heathland was set up by de Smidt in the early 1960s (de Smidt 1966) and extended with study of the inland and coastal sand dunes in the mid-1960s. The cryptogam richness of these ecotopes was studied in detail by Oostra (1968) and Sipman (1969) for the coastal dunes, and by Daniëls (1983) and Pos (1968) for the inland dunes. 1.2. Changes in sand dune vegetation since the 1970s Since the 1970s, nitrogen (NH4-N, NO3-N and organic compounds) has been an important acidifying and eutrophicating pollutant throughout the Netherlands as a 3 result of the increased dry and wet atmospheric deposition. Nutrient enrichment increases the productivity in nutrient-poor ecosystems, enabling more competitive species to oust species that are characteristic of these ecosystems (Bobbink et al. 1998). In the calcium-poor coastal dunes this became apparent in the dominance of tall graminoids, especially Ammophila arenaria, which changed the aspect of the vegetation (Ketner-Oostra 1993), while other grasses dominated the vegetation of inland sand dunes (Masselink 1994) and heathlands (Diemont 1996). Changes in the flora, both of phanerophytes and cryptogams, in dry oligotrophic habitats, have been partly correlated with acidification caused by the high emission of SO2 (Quené-Boterenbrood 1988). That emission declined considerably from the end of the 1970s onwards. However, since then, nitrogen (N) deposition has been the main polluting factor, partly as an effect of intensified livestock farming. In the central part of the country in 1990 the mean nitrogen deposition was 50 kg N ha-1 and for the West Frisian islands it was estimated to be 20 kg N ha-1 (Bleeker & Erisman 1996). From 1990 N deposition gradually decreased, to a mean value of 40 kg N ha-1 in 2001, but near areas with high livestock concentrations the N deposition is still high, with peak values exceeding 60 kg N ha-1 yr-1 (Buijsman 2004). In the inland sand dunes the decrease in surface area of dry oligotrophic ecotopes was accompanied by an increase of the abundance and size of graminoids. Berendse et al. (1993) pointed to an accelerated vegetation succession on nutrient- poor sandy soils as one of the effects of N deposition. Another effect was that mosses became dominant (Daniëls et al. 1987). The neophytic moss Campylopus introflexus, a species adapted to acid open sand, invaded both coastal and inland dunes and reduced the area of open sand and the lichen richness in both ecotopes (van der Meulen et al. 1987; Biermann & Daniëls 1997). In the 1990s the State Forestry Service Region Veluwe-Achterhoek showed interest in the current lichen- diversity and the lichen communities on the Kootwijkerzand and I was assigned to their vegetation study combined with that of the soil. This resulted in setting out Permanent quadrats (PQs) in these lichen communities (Figure 6.1a) and in 1993 the monitoring of the vegetation development began (Ketner-Oostra 1994). 1.3. EGM (= Effect-oriented Management Measures) in coastal dunes In the mid-1980s, an explicit objective of Dutch nature conservation policy was to halt the decline in biodiversity. However, attempts to reverse the influence of acidification and eutrophication in natural landscapes were rarely successful. In 1989 the Ministry of Agriculture, Nature and Fisheries began to fund restoration practices. A survival plan for forests and nature ('Overlevingsplan Bos en Natuur' (OBN) 1995-2010 was launched (LNV 1994) and an Expert Network for Coastal and Inland sand dunes was set up to advise on new restoration measures. Since then, 'Effect-oriented Management Measures' (EGM), i.e. additional restoration measures against acidification, eutrophication and desiccation in different nature target types, have been funded. Part of the available budget has been used for knowledge development. 4 Calcium-poor coastal dunes were included in a nation-wide EGM research project that aimed to restore former biodiversity in dry dunes (Vertegaal et al. 1991). In phase 1 (1991-1995) the University of Amsterdam (Department of Physical Geography and Soil Research) implemented large-scale management in 15 former blow-outs in the dune area of Eldorado on the island of Terschelling. In the final report on phase 1 van der Meulen et al. (1996) concluded that elongating the blow- outs in the direction of the prevailing westerly wind was particularly successful. The superficial layer of the accumulated sand proved to be neutral (pH-CaCl 7.1- 7.8) and a pioneer vegetation established. However, the duration of the period in which sand was still blowing seemed restricted. Veer (1997) did small-scale experiments with mowing, sod-cutting and sand suppletion in open Violo- Corynephoretum and grass encroached V.-C. in plots of dune grassland on Terschelling. She found that atmospheric nitrogen input was an important source of N in open V.-C., but in grass-dominated V.-C. plots it was largely exceeded by mineralization. Kooijman et al. (1998) found that in the calcium-poor dune sands of the Wadden district, phosphorus was available, but N was limited; atmospheric N input had much more effect here than in the calcium-rich dunes of the Renodunale district, where phosphorus availability was limited. 1.4. Small-scale restoration measures in inland sand dunes before 1990 Since the 1960s, the sand dune management has been mainly small scale. Foresters have felled self-sown trees or a few ha of pinewood with chainsaws. One of the fieldwork areas for this thesis, the Kootwijkerzand, has been managed this way by the State Forestry (see Daniëls & Krüger 1996; Ketner-Oostra & Huijsman 1998). Small-scale management has also been practised in the Hulshorsterzand (owned by Natuurmonumenten), the Wekeromse Zand (Het Geldersch Landschap) and De Hoge Veluwe National Park (Daniëls & Krüger 1996). In the Harskamperzand, the army burn dry grassland and heath as a precaution against fires starting during their shooting exercises (Haveman et al.